<?php

/**
 * Class FinderPatternFinder
 *
 * @created      17.01.2021
 *
 * @author       ZXing Authors
 * @author       Smiley <smiley@chillerlan.net>
 * @copyright    2021 Smiley
 * @license      Apache-2.0
 */
declare(strict_types=1);

namespace zxf\QrCode\Detector;

use const PHP_FLOAT_MAX;

use zxf\QrCode\Decoder\BitMatrix;

use function abs;
use function count;
use function intdiv;
use function usort;

/**
 * This class attempts to find finder patterns in a QR Code. Finder patterns are the square
 * markers at three corners of a QR Code.
 *
 * This class is thread-safe but not reentrant. Each thread must allocate its own object.
 *
 * @author Sean Owen
 */
final class FinderPatternFinder
{
    private const MIN_SKIP = 2;

    private const MAX_MODULES = 177; // 1 pixel/module times 3 modules/center

    private const CENTER_QUORUM = 2; // support up to version 10 for mobile clients

    private BitMatrix $matrix;

    /** @var \zxf\QrCode\Detector\FinderPattern[] */
    private array $possibleCenters;

    private bool $hasSkipped = false;

    /**
     * Creates a finder that will search the image for three finder patterns.
     *
     * @param  BitMatrix  $matrix  image to search
     */
    public function __construct(BitMatrix $matrix)
    {
        $this->matrix = $matrix;
        $this->possibleCenters = [];
    }

    /**
     * @return \zxf\QrCode\Detector\FinderPattern[]
     */
    public function find(): array
    {
        $dimension = $this->matrix->getSize();

        // We are looking for black/white/black/white/black modules in
        // 1:1:3:1:1 ratio; this tracks the number of such modules seen so far
        // Let's assume that the maximum version QR Code we support takes up 1/4 the height of the
        // image, and then account for the center being 3 modules in size. This gives the smallest
        // number of pixels the center could be, so skip this often.
        $iSkip = intdiv((3 * $dimension), (4 * self::MAX_MODULES));

        if ($iSkip < self::MIN_SKIP) {
            $iSkip = self::MIN_SKIP;
        }

        $done = false;

        for ($i = ($iSkip - 1); ($i < $dimension) && ! $done; $i += $iSkip) {
            // Get a row of black/white values
            $stateCount = $this->getCrossCheckStateCount();
            $currentState = 0;

            for ($j = 0; $j < $dimension; $j++) {

                // Black pixel
                if ($this->matrix->check($j, $i)) {
                    // Counting white pixels
                    if (($currentState & 1) === 1) {
                        $currentState++;
                    }

                    $stateCount[$currentState]++;
                }
                // White pixel
                else {
                    // Counting black pixels
                    if (($currentState & 1) === 0) {
                        // A winner?
                        if ($currentState === 4) {
                            // Yes
                            if ($this->foundPatternCross($stateCount)) {
                                $confirmed = $this->handlePossibleCenter($stateCount, $i, $j);

                                if ($confirmed) {
                                    // Start examining every other line. Checking each line turned out to be too
                                    // expensive and didn't improve performance.
                                    $iSkip = 3;

                                    if ($this->hasSkipped) {
                                        $done = $this->haveMultiplyConfirmedCenters();
                                    } else {
                                        $rowSkip = $this->findRowSkip();

                                        if ($rowSkip > $stateCount[2]) {
                                            // Skip rows between row of lower confirmed center
                                            // and top of presumed third confirmed center
                                            // but back up a bit to get a full chance of detecting
                                            // it, entire width of center of finder pattern

                                            // Skip by rowSkip, but back off by $stateCount[2] (size of last center
                                            // of pattern we saw) to be conservative, and also back off by iSkip which
                                            // is about to be re-added
                                            $i += ($rowSkip - $stateCount[2] - $iSkip);
                                            $j = ($dimension - 1);
                                        }
                                    }
                                } else {
                                    $stateCount = $this->doShiftCounts2($stateCount);
                                    $currentState = 3;

                                    continue;
                                }
                                // Clear state to start looking again
                                $currentState = 0;
                                $stateCount = $this->getCrossCheckStateCount();
                            }
                            // No, shift counts back by two
                            else {
                                $stateCount = $this->doShiftCounts2($stateCount);
                                $currentState = 3;
                            }
                        } else {
                            $stateCount[++$currentState]++;
                        }
                    }
                    // Counting white pixels
                    else {
                        $stateCount[$currentState]++;
                    }
                }
            }

            if ($this->foundPatternCross($stateCount)) {
                $confirmed = $this->handlePossibleCenter($stateCount, $i, $dimension);

                if ($confirmed) {
                    $iSkip = $stateCount[0];

                    if ($this->hasSkipped) {
                        // Found a third one
                        $done = $this->haveMultiplyConfirmedCenters();
                    }
                }
            }
        }

        return $this->orderBestPatterns($this->selectBestPatterns());
    }

    /**
     * @return int[]
     */
    private function getCrossCheckStateCount(): array
    {
        return [0, 0, 0, 0, 0];
    }

    /**
     * @param  int[]  $stateCount
     * @return int[]
     */
    private function doShiftCounts2(array $stateCount): array
    {
        $stateCount[0] = $stateCount[2];
        $stateCount[1] = $stateCount[3];
        $stateCount[2] = $stateCount[4];
        $stateCount[3] = 1;
        $stateCount[4] = 0;

        return $stateCount;
    }

    /**
     * Given a count of black/white/black/white/black pixels just seen and an end position,
     * figures the location of the center of this run.
     *
     * @param  int[]  $stateCount
     */
    private function centerFromEnd(array $stateCount, int $end): float
    {
        return (float) (($end - $stateCount[4] - $stateCount[3]) - $stateCount[2] / 2);
    }

    /**
     * @param  int[]  $stateCount
     */
    private function foundPatternCross(array $stateCount): bool
    {
        // Allow less than 50% variance from 1-1-3-1-1 proportions
        return $this->foundPatternVariance($stateCount, 2.0);
    }

    /**
     * @param  int[]  $stateCount
     */
    private function foundPatternDiagonal(array $stateCount): bool
    {
        // Allow less than 75% variance from 1-1-3-1-1 proportions
        return $this->foundPatternVariance($stateCount, 1.333);
    }

    /**
     * @param  int[]  $stateCount  count of black/white/black/white/black pixels just read
     * @return bool true if the proportions of the counts is close enough to the 1/1/3/1/1 ratios
     *              used by finder patterns to be considered a match
     */
    private function foundPatternVariance(array $stateCount, float $variance): bool
    {
        $totalModuleSize = 0;

        for ($i = 0; $i < 5; $i++) {
            $count = $stateCount[$i];

            if ($count === 0) {
                return false;
            }

            $totalModuleSize += $count;
        }

        if ($totalModuleSize < 7) {
            return false;
        }

        $moduleSize = ($totalModuleSize / 7.0);
        $maxVariance = ($moduleSize / $variance);

        return
            abs($moduleSize - $stateCount[0]) < $maxVariance
            && abs($moduleSize - $stateCount[1]) < $maxVariance
            && abs(3.0 * $moduleSize - $stateCount[2]) < (3 * $maxVariance)
            && abs($moduleSize - $stateCount[3]) < $maxVariance
            && abs($moduleSize - $stateCount[4]) < $maxVariance;
    }

    /**
     * After a vertical and horizontal scan finds a potential finder pattern, this method
     * "cross-cross-cross-checks" by scanning down diagonally through the center of the possible
     * finder pattern to see if the same proportion is detected.
     *
     * @param  int  $centerI  row where a finder pattern was detected
     * @param  int  $centerJ  center of the section that appears to cross a finder pattern
     * @return bool true if proportions are withing expected limits
     */
    private function crossCheckDiagonal(int $centerI, int $centerJ): bool
    {
        $stateCount = $this->getCrossCheckStateCount();

        // Start counting up, left from center finding black center mass
        $i = 0;

        while ($centerI >= $i && $centerJ >= $i && $this->matrix->check(($centerJ - $i), ($centerI - $i))) {
            $stateCount[2]++;
            $i++;
        }

        if ($stateCount[2] === 0) {
            return false;
        }

        // Continue up, left finding white space
        while ($centerI >= $i && $centerJ >= $i && ! $this->matrix->check(($centerJ - $i), ($centerI - $i))) {
            $stateCount[1]++;
            $i++;
        }

        if ($stateCount[1] === 0) {
            return false;
        }

        // Continue up, left finding black border
        while ($centerI >= $i && $centerJ >= $i && $this->matrix->check(($centerJ - $i), ($centerI - $i))) {
            $stateCount[0]++;
            $i++;
        }

        if ($stateCount[0] === 0) {
            return false;
        }

        $dimension = $this->matrix->getSize();

        // Now also count down, right from center
        $i = 1;
        // phpcs:ignore
        while (($centerI + $i) < $dimension && ($centerJ + $i) < $dimension && $this->matrix->check(($centerJ + $i), ($centerI + $i))) {
            $stateCount[2]++;
            $i++;
        }

        // phpcs:ignore
        while (($centerI + $i) < $dimension && ($centerJ + $i) < $dimension && ! $this->matrix->check(($centerJ + $i), ($centerI + $i))) {
            $stateCount[3]++;
            $i++;
        }

        if ($stateCount[3] === 0) {
            return false;
        }

        // phpcs:ignore
        while (($centerI + $i) < $dimension && ($centerJ + $i) < $dimension && $this->matrix->check(($centerJ + $i), ($centerI + $i))) {
            $stateCount[4]++;
            $i++;
        }

        if ($stateCount[4] === 0) {
            return false;
        }

        return $this->foundPatternDiagonal($stateCount);
    }

    /**
     * After a horizontal scan finds a potential finder pattern, this method
     * "cross-checks" by scanning down vertically through the center of the possible
     * finder pattern to see if the same proportion is detected.
     *
     * $startI   row where a finder pattern was detected
     * $centerJ  center of the section that appears to cross a finder pattern
     * $maxCount maximum reasonable number of modules that should be
     *           observed in any reading state, based on the results of the horizontal scan
     * $originalStateCountTotal
     *
     * returns vertical center of finder pattern, or null if not found
     *
     * @noinspection DuplicatedCode
     */
    private function crossCheckVertical(int $startI, int $centerJ, int $maxCount, int $originalStateCountTotal): ?float
    {
        $maxI = $this->matrix->getSize();
        $stateCount = $this->getCrossCheckStateCount();

        // Start counting up from center
        $i = $startI;
        while ($i >= 0 && $this->matrix->check($centerJ, $i)) {
            $stateCount[2]++;
            $i--;
        }

        if ($i < 0) {
            return null;
        }

        while ($i >= 0 && ! $this->matrix->check($centerJ, $i) && $stateCount[1] <= $maxCount) {
            $stateCount[1]++;
            $i--;
        }

        // If already too many modules in this state or ran off the edge:
        if ($i < 0 || $stateCount[1] > $maxCount) {
            return null;
        }

        while ($i >= 0 && $this->matrix->check($centerJ, $i) && $stateCount[0] <= $maxCount) {
            $stateCount[0]++;
            $i--;
        }

        if ($stateCount[0] > $maxCount) {
            return null;
        }

        // Now also count down from center
        $i = ($startI + 1);
        while ($i < $maxI && $this->matrix->check($centerJ, $i)) {
            $stateCount[2]++;
            $i++;
        }

        if ($i === $maxI) {
            return null;
        }

        while ($i < $maxI && ! $this->matrix->check($centerJ, $i) && $stateCount[3] < $maxCount) {
            $stateCount[3]++;
            $i++;
        }

        if ($i === $maxI || $stateCount[3] >= $maxCount) {
            return null;
        }

        while ($i < $maxI && $this->matrix->check($centerJ, $i) && $stateCount[4] < $maxCount) {
            $stateCount[4]++;
            $i++;
        }

        if ($stateCount[4] >= $maxCount) {
            return null;
        }

        // If we found a finder-pattern-like section, but its size is more than 40% different from
        // the original, assume it's a false positive
        $stateCountTotal = ($stateCount[0] + $stateCount[1] + $stateCount[2] + $stateCount[3] + $stateCount[4]);

        if ((5 * abs($stateCountTotal - $originalStateCountTotal)) >= (2 * $originalStateCountTotal)) {
            return null;
        }

        if (! $this->foundPatternCross($stateCount)) {
            return null;
        }

        return $this->centerFromEnd($stateCount, $i);
    }

    /**
     * Like #crossCheckVertical(int, int, int, int), and in fact is basically identical,
     * except it reads horizontally instead of vertically. This is used to cross-cross
     * check a vertical cross-check and locate the real center of the alignment pattern.
     *
     * @noinspection DuplicatedCode
     */
    private function crossCheckHorizontal(int $startJ, int $centerI, int $maxCount, int $originalStateCountTotal): ?float
    {
        $maxJ = $this->matrix->getSize();
        $stateCount = $this->getCrossCheckStateCount();

        $j = $startJ;
        while ($j >= 0 && $this->matrix->check($j, $centerI)) {
            $stateCount[2]++;
            $j--;
        }

        if ($j < 0) {
            return null;
        }

        while ($j >= 0 && ! $this->matrix->check($j, $centerI) && $stateCount[1] <= $maxCount) {
            $stateCount[1]++;
            $j--;
        }

        if ($j < 0 || $stateCount[1] > $maxCount) {
            return null;
        }

        while ($j >= 0 && $this->matrix->check($j, $centerI) && $stateCount[0] <= $maxCount) {
            $stateCount[0]++;
            $j--;
        }

        if ($stateCount[0] > $maxCount) {
            return null;
        }

        $j = ($startJ + 1);
        while ($j < $maxJ && $this->matrix->check($j, $centerI)) {
            $stateCount[2]++;
            $j++;
        }

        if ($j === $maxJ) {
            return null;
        }

        while ($j < $maxJ && ! $this->matrix->check($j, $centerI) && $stateCount[3] < $maxCount) {
            $stateCount[3]++;
            $j++;
        }

        if ($j === $maxJ || $stateCount[3] >= $maxCount) {
            return null;
        }

        while ($j < $maxJ && $this->matrix->check($j, $centerI) && $stateCount[4] < $maxCount) {
            $stateCount[4]++;
            $j++;
        }

        if ($stateCount[4] >= $maxCount) {
            return null;
        }

        // If we found a finder-pattern-like section, but its size is significantly different from
        // the original, assume it's a false positive
        $stateCountTotal = ($stateCount[0] + $stateCount[1] + $stateCount[2] + $stateCount[3] + $stateCount[4]);

        if ((5 * abs($stateCountTotal - $originalStateCountTotal)) >= $originalStateCountTotal) {
            return null;
        }

        if (! $this->foundPatternCross($stateCount)) {
            return null;
        }

        return $this->centerFromEnd($stateCount, $j);
    }

    /**
     * This is called when a horizontal scan finds a possible alignment pattern. It will
     * cross-check with a vertical scan, and if successful, will, ah, cross-cross-check
     * with another horizontal scan. This is needed primarily to locate the real horizontal
     * center of the pattern in cases of extreme skew.
     * And then we cross-cross-cross check with another diagonal scan.
     *
     * If that succeeds the finder pattern location is added to a list that tracks
     * the number of times each location has been nearly-matched as a finder pattern.
     * Each additional find is more evidence that the location is in fact a finder
     * pattern center
     *
     * @param  int[]  $stateCount  reading state module counts from horizontal scan
     * @param  int  $i  row where finder pattern may be found
     * @param  int  $j  end of possible finder pattern in row
     * @return bool if a finder pattern candidate was found this time
     */
    private function handlePossibleCenter(array $stateCount, int $i, int $j): bool
    {
        $stateCountTotal = ($stateCount[0] + $stateCount[1] + $stateCount[2] + $stateCount[3] + $stateCount[4]);
        $centerJ = $this->centerFromEnd($stateCount, $j);
        $centerI = $this->crossCheckVertical($i, (int) $centerJ, $stateCount[2], $stateCountTotal);

        if ($centerI !== null) {
            // Re-cross check
            $centerJ = $this->crossCheckHorizontal((int) $centerJ, (int) $centerI, $stateCount[2], $stateCountTotal);
            if ($centerJ !== null && ($this->crossCheckDiagonal((int) $centerI, (int) $centerJ))) {
                $estimatedModuleSize = ($stateCountTotal / 7.0);
                $found = false;

                // cautious (was in for fool in which $this->possibleCenters is updated)
                $count = count($this->possibleCenters);

                for ($index = 0; $index < $count; $index++) {
                    $center = $this->possibleCenters[$index];
                    // Look for about the same center and module size:
                    if ($center->aboutEquals($estimatedModuleSize, $centerI, $centerJ)) {
                        $this->possibleCenters[$index] = $center->combineEstimate($centerI, $centerJ, $estimatedModuleSize);
                        $found = true;
                        break;
                    }
                }

                if (! $found) {
                    $point = new FinderPattern($centerJ, $centerI, $estimatedModuleSize);
                    $this->possibleCenters[] = $point;
                }

                return true;
            }
        }

        return false;
    }

    /**
     * @return int number of rows we could safely skip during scanning, based on the first
     *             two finder patterns that have been located. In some cases their position will
     *             allow us to infer that the third pattern must lie below a certain point farther
     *             down in the image.
     */
    private function findRowSkip(): int
    {
        $max = count($this->possibleCenters);

        if ($max <= 1) {
            return 0;
        }

        $firstConfirmedCenter = null;

        foreach ($this->possibleCenters as $center) {

            if ($center->getCount() >= self::CENTER_QUORUM) {

                if ($firstConfirmedCenter === null) {
                    $firstConfirmedCenter = $center;
                } else {
                    // We have two confirmed centers
                    // How far down can we skip before resuming looking for the next
                    // pattern? In the worst case, only the difference between the
                    // difference in the x / y coordinates of the two centers.
                    // This is the case where you find top left last.
                    $this->hasSkipped = true;

                    return (int) ((abs($firstConfirmedCenter->getX() - $center->getX()) -
                                  abs($firstConfirmedCenter->getY() - $center->getY())) / 2);
                }
            }
        }

        return 0;
    }

    /**
     * @return bool true if we have found at least 3 finder patterns that have been detected
     *              at least #CENTER_QUORUM times each, and, the estimated module size of the
     *              candidates is "pretty similar"
     */
    private function haveMultiplyConfirmedCenters(): bool
    {
        $confirmedCount = 0;
        $totalModuleSize = 0.0;
        $max = count($this->possibleCenters);

        foreach ($this->possibleCenters as $pattern) {
            if ($pattern->getCount() >= self::CENTER_QUORUM) {
                $confirmedCount++;
                $totalModuleSize += $pattern->getEstimatedModuleSize();
            }
        }

        if ($confirmedCount < 3) {
            return false;
        }
        // OK, we have at least 3 confirmed centers, but, it's possible that one is a "false positive"
        // and that we need to keep looking. We detect this by asking if the estimated module sizes
        // vary too much. We arbitrarily say that when the total deviation from average exceeds
        // 5% of the total module size estimates, it's too much.
        $average = ($totalModuleSize / (float) $max);
        $totalDeviation = 0.0;

        foreach ($this->possibleCenters as $pattern) {
            $totalDeviation += abs($pattern->getEstimatedModuleSize() - $average);
        }

        return $totalDeviation <= (0.05 * $totalModuleSize);
    }

    /**
     * @return \zxf\QrCode\Detector\FinderPattern[] the 3 best FinderPatterns from our list of candidates. The "best" are
     *                                              those that have been detected at least #CENTER_QUORUM times, and whose module
     *                                              size differs from the average among those patterns the least
     *
     * @throws \zxf\QrCode\Detector\QRCodeDetectorException if 3 such finder patterns do not exist
     */
    private function selectBestPatterns(): array
    {
        $startSize = count($this->possibleCenters);

        if ($startSize < 3) {
            throw new QRCodeDetectorException('could not find enough finder patterns');
        }

        usort(
            $this->possibleCenters,
            fn (FinderPattern $a, FinderPattern $b) => ($a->getEstimatedModuleSize() <=> $b->getEstimatedModuleSize()),
        );

        $distortion = PHP_FLOAT_MAX;
        $bestPatterns = [];

        for ($i = 0; $i < ($startSize - 2); $i++) {
            $fpi = $this->possibleCenters[$i];
            $minModuleSize = $fpi->getEstimatedModuleSize();

            for ($j = ($i + 1); $j < ($startSize - 1); $j++) {
                $fpj = $this->possibleCenters[$j];
                $squares0 = $fpi->getSquaredDistance($fpj);

                for ($k = ($j + 1); $k < $startSize; $k++) {
                    $fpk = $this->possibleCenters[$k];
                    $maxModuleSize = $fpk->getEstimatedModuleSize();

                    // module size is not similar
                    if ($maxModuleSize > ($minModuleSize * 1.4)) {
                        continue;
                    }

                    $a = $squares0;
                    $b = $fpj->getSquaredDistance($fpk);
                    $c = $fpi->getSquaredDistance($fpk);

                    // sorts ascending - inlined
                    if ($a < $b) {
                        if ($b > $c) {
                            if ($a < $c) {
                                $temp = $b;
                                $b = $c;
                                $c = $temp;
                            } else {
                                $temp = $a;
                                $a = $c;
                                $c = $b;
                                $b = $temp;
                            }
                        }
                    } else {
                        if ($b < $c) {
                            if ($a < $c) {
                                $temp = $a;
                                $a = $b;
                                $b = $temp;
                            } else {
                                $temp = $a;
                                $a = $b;
                                $b = $c;
                                $c = $temp;
                            }
                        } else {
                            $temp = $a;
                            $a = $c;
                            $c = $temp;
                        }
                    }

                    // a^2 + b^2 = c^2 (Pythagorean theorem), and a = b (isosceles triangle).
                    // Since any right triangle satisfies the formula c^2 - b^2 - a^2 = 0,
                    // we need to check both two equal sides separately.
                    // The value of |c^2 - 2 * b^2| + |c^2 - 2 * a^2| increases as dissimilarity
                    // from isosceles right triangle.
                    $d = (abs($c - 2 * $b) + abs($c - 2 * $a));

                    if ($d < $distortion) {
                        $distortion = $d;
                        $bestPatterns = [$fpi, $fpj, $fpk];
                    }
                }
            }
        }

        if ($distortion === PHP_FLOAT_MAX) {
            throw new QRCodeDetectorException('finder patterns may be too distorted');
        }

        return $bestPatterns;
    }

    /**
     * Orders an array of three ResultPoints in an order [A,B,C] such that AB is less than AC
     * and BC is less than AC, and the angle between BC and BA is less than 180 degrees.
     *
     * @param  \zxf\QrCode\Detector\FinderPattern[]  $patterns  array of three FinderPattern to order
     * @return \zxf\QrCode\Detector\FinderPattern[]
     */
    private function orderBestPatterns(array $patterns): array
    {

        // Find distances between pattern centers
        $zeroOneDistance = $patterns[0]->getDistance($patterns[1]);
        $oneTwoDistance = $patterns[1]->getDistance($patterns[2]);
        $zeroTwoDistance = $patterns[0]->getDistance($patterns[2]);

        // Assume one closest to other two is B; A and C will just be guesses at first
        if ($oneTwoDistance >= $zeroOneDistance && $oneTwoDistance >= $zeroTwoDistance) {
            [$pointB, $pointA, $pointC] = $patterns;
        } elseif ($zeroTwoDistance >= $oneTwoDistance && $zeroTwoDistance >= $zeroOneDistance) {
            [$pointA, $pointB, $pointC] = $patterns;
        } else {
            [$pointA, $pointC, $pointB] = $patterns;
        }

        // Use cross product to figure out whether A and C are correct or flipped.
        // This asks whether BC x BA has a positive z component, which is the arrangement
        // we want for A, B, C. If it's negative, then we've got it flipped around and
        // should swap A and C.
        if ($this->crossProductZ($pointA, $pointB, $pointC) < 0.0) {
            $temp = $pointA;
            $pointA = $pointC;
            $pointC = $temp;
        }

        return [$pointA, $pointB, $pointC];
    }

    /**
     * Returns the z component of the cross product between vectors BC and BA.
     */
    private function crossProductZ(FinderPattern $pointA, FinderPattern $pointB, FinderPattern $pointC): float
    {
        $bX = $pointB->getX();
        $bY = $pointB->getY();

        return (($pointC->getX() - $bX) * ($pointA->getY() - $bY)) - (($pointC->getY() - $bY) * ($pointA->getX() - $bX));
    }
}
